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Interconnections in multichip modules, because of their lengths and signal frequencies, usually operate in the near-transmission-line regime. Their small cross-sectional area, dictated by the need for high wiring density, leads to lines that are necessarily lossy. In this paper, we present an analysis of lossy transmission-line interconnections that determines the minimum loss needed to obtain stable signal propagation in unterminated lines. This analysis leads to a simple, robust design criterion that can be easily applied to most multichip module circuits. We present an example of this approach for a particular module structure, and discuss the operating limits imposed by this method.

Cathodoluminescence scanning electron microscopy is used to study AlxGa1-x As epilayers grown on a nonplanar substrate by molecular beam epitaxy. Grooves parallel to the [011] direction were etched in an undoped GaAs substrate. Growth on such grooves proceeds on particular facet planes. We find that the aluminum concentration in the epilayers is dependent on the facet orientation, changing by as much as 35% from the value in the unpatterned areas. The transition in the aluminum concentration at a boundary between two facets is observed to be very abrupt. [ABSTRACT FROM AUTHOR]

We report the first observation of a lateral junction formed in an alloy due to an abrupt transition from segregated to random AlGaAs alloy compositions. Al0.25Ga0.75As epilayers were grown by molecular beam epitaxy on [011] oriented grooves in a nonplanar (100) GaAs substrate. A quasi-periodic modulation of the aluminum concentration occurs spontaneously in material grown on the (111) facets of the groove, with a period of 50–70 Å along the [111] direction. The compositional modulation is associated with a reduction of the band gap by 130 meV, with respect to the random alloy. While segregation of the AlGaAs alloy has been seen previously, this is the first observation of segregation of AlGaAs grown on a (111) surface. The compositional modulation terminates abruptly at the boundaries of the (111) facet, forming abrupt lateral junctions in the AlGaAs layers grown on a groove. [ABSTRACT FROM AUTHOR]